The present invention relates to the structure of the rotor of an electric motor for a compressor.
Conventional rotors of electric motors for a compressor generally has the following structures.
The rotor described in Japanese Patent Laid-Open No. 52359/1982 is produced by inserting a laminated rotor core and magnetic materials into a metal pipe, and integrally die-casting these elements.
The rotor described in Japanese Patent Laid-Open No. 246748/1990 is produced by inserting a laminated rotor core and magnetic materials into a metal pipe in the same way as in the above-described rotor, and integrally clamping these elements. At the time of clamping, an air gap portion is provided between adjacent magnetic materials so as to safely separate the poles of the magnetic materials, thereby enhancing the efficiency.
Another rotor is described in Japanese Patent Publication No. 23584/1985. In this rotor, magnetic materials which constitute the magnetic poles are inserted (embedded) into the rotor core. This rotor is used for a synchronous motor which is capable of self starting.
Japanese Patent Laid-Open No. 185247/1992 discloses another rotor, which is composed of magnetic materials embedded into the salient pole portions of the rotor core Which has a salient-pole structure. The rotor core with the magnetic materials embedded therein and end surface members for covering both end surface thereof are arranged, and a rotary shaft is integrally press-fitted into the rotor core in this state.
The conventional rotors having the above-described structures, however, have problems such as much eddy current loss caused by the cage portion of a die-cast material (e.g., zinc and aluminum), eddy current loss in a metal pipe, and difficulty in the maintenance of the high dimensional accuracy at the time of production due to the projection provided on the rotor core so as to prevent the movement of the magnetic materials.
In the rotor provided with air gaps for separating poles, when a breakage such as cracking is produced on the magnetic material (especially, ferrite) due to a thermal shock or a mechanical shock applied to the rotor, the fragments of the magnetic material flow into the air gaps, which sometimes leads to a further breakage or chipping.
In some rotors, an eddy current is produced by the secondary conductor in the rotor core, and since part of the magnetic flux produced from the magnetic material is short-circuited in the rotor core (conductor), the operation efficiency of the motor is lowered.
Other rotors suffer from problems such as the loosening of the rotor core and difficulty in the maintenance of the high dimensional accuracy due to the low accuracy of assembly in the process of press-fitting the rotary shaft of the motor.